1. Field of the Inventions
The present application relates to steering damping methods and devices for a vehicle in which impact force applied to a steering member is damped by damping force generated cooperatively with a steering operation of the steering member as well as methods and systems in which strength of the damping force is varied according to a running state of the vehicle.
2. Description of the Related Art
Japanese Patent Documents JP-A-2003-237672 and JP-A-2004-26092 disclose conventional steering damping devices which dampen the impact force applied to a steering member from a road surface to improve driving stability of a vehicle.
These patents disclose a steering damper which performs an expansion operation and a contraction operation cooperatively with a steering operation of the steering member and use hydraulic oil flow to generate the damping forces. These documents also further disclose a bypass oil passage mutually connecting two oil chambers defined by a piston in a cylinder of the steering damper. They additionally disclose a ball disposed in a middle part of the bypass oil passage configured to open and close the bypass oil passage.
When the steering damper is operated cooperatively with the steering operation of the steering member, the hydraulic oil flows through the bypass oil passage from one side of the two oil chambers to the other side thereof. In addition, the ball mechanically opens or closes the bypass oil passage according to the strength of external force applied to the ball from the hydraulic oil.
With reference to FIG. 5, when the ball opens the bypass oil passage, the hydraulic oil freely flows through the bypass oil passage. Therefore, on this occasion, the steering damper has a damping force characteristic 1 in which relatively small, first damping force is generated. On the other hand, when the ball closes the bypass oil passage, the hydraulic oil is restrained from flowing through the bypass oil passage. Therefore, on this occasion, the steering damper has a damping force characteristic 2 in which a larger, second damping force is generated.
While the vehicle is running, and when the road surface is generally flat, the impact force applied to the steering member from the road surface is relatively small in general. Therefore, the steering operation of the steering member is relatively slow. Consequently, driving stability is kept excellent. Further, on this occasion, an operational speed of the steering damper cooperating with the steering member is lower than a predetermined value. Therefore, the external force applied to the ball from the hydraulic oil flowing through the bypass oil passage is relatively small. Accordingly, the ball keeps the bypass oil passage open. In this manner, the steering damper generates damping force according to the damping force characteristic 1 of the steering damper.
Consequently, as described above, when the road surface is generally flat, driving stability is kept excellent, and a steering operation by a rider in relation to the steering member is not intensely affected by the damping force of the steering damper, and can be performed lightly and smoothly. Therefore, ride comfort of the vehicle is also kept excellent.
On the other hand, when the road surface is rough with more unevenness, the impact force applied to the steering member from the road surface is relatively large. Therefore, the steering operation of the steering member by the impact force is faster than when the road surface is generally flat. Consequently, the operational speed of the steering damper cooperating with the steering member becomes equal to or higher than the predetermined value. Therefore, the external force applied to the ball from the hydraulic oil flowing through the bypass oil passage becomes larger than when the road surface is generally flat. Accordingly, the ball mechanically closes the bypass oil passage with the external force. In this manner, the steering damper generates damping force according to the damping force characteristic 2 of the steering damper.
Consequently, as described above, when the road surface is rough, the impact force applied to the steering member is damped by the larger damping force. Accordingly, a faster steering operation is regulated, and driving stability is kept excellent.